I am fairly new and need to know how to ascend up into the atmosphere. I have a Radon-Ulzer 620C which I know should be able to ascend. Anytime I try to click the 'Ascend' button, it just reloads the same screen. Even after I waited for over an hour it remains the same. What is wrong, and what should happen when I click the button?

Actually, a Radon-Ulzer isn't able to ascend into the atmosphere (imagine the atmosphere layer being the one where airplanes travel, i.e. at a hight of around 11km).
Check the vehicle rules page for details on which vehicles can ascend into atmosphere and which can't.